1. Field of the Invention
The present invention concerns a magnetic resonance apparatus of the type having a transmission and reception (RF) coil system and a gradient coil system that is designed to generate a gradient field that is periodic in one spatial direction, wherein the gradient field and/or the examination subject can be displaced in the spatial direction of the periodicity to produce a relative position change between the periodic gradient field and the examination subject.
2. Description of the Prior Art
In order to shorten the measurement (data acquisition) time in magnetic resonance apparatuses so that more patients can be examined with a single apparatus and the time of residence for the individual patients in the scanner is decreased, a conventional approach has been to increase the gradient field strengths and to shorten the switching times. There are limits to this procedure because (due to conductivity in the tissue of the patient) voltages can be induced that are sensed as painful or manifest themselves in uncomfortable muscle convulsions. In order to prevent such stimulations but use a very short measurement time, it is known from DE 198 43 463 C2 to use a magnetic field gradient that is periodic in one spatial direction. The gradient field described therein proposed exhibits a field curve that is generally sinusoidal but is flat in places, such that in these regions no spatial resolution can be achieved, for which it is proposed to implement a further measurement with a gradient field displaced in the spatial direction of the periodicity. This displacement can also be achieved in the examination subject being displaced in the spatial direction of the periodicity.
Due to the rising and falling edges of such periodic gradient fields, however, dual possibilities exist with regard to the spatial association, which must be addressed by suitable measures. In this context, from DE 198 43 463 C2 it is known to associate various segments in the spatial direction of the periodicity with respective separate sub-systems of an antenna system for transmission or reception. The spatial selection that can be achieved in such an arrangement, however, is limited.